<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8">
</head>
<body text="#000000" bgcolor="#FFFFFF">
Forwarding message from Todd with estimates about convergence <br>
of the beam near collimator. <br>
<div class="moz-forward-container"><br>
<br>
-------- Forwarded Message --------
<table class="moz-email-headers-table" border="0" cellpadding="0"
cellspacing="0">
<tbody>
<tr>
<th align="RIGHT" valign="BASELINE" nowrap="nowrap">Subject:
</th>
<td>5C11/5C11B/radiator harp scan fitting</td>
</tr>
<tr>
<th align="RIGHT" valign="BASELINE" nowrap="nowrap">Date: </th>
<td>Wed, 13 Apr 2016 15:20:31 -0400</td>
</tr>
<tr>
<th align="RIGHT" valign="BASELINE" nowrap="nowrap">From: </th>
<td>Todd Satogata <a class="moz-txt-link-rfc2396E" href="mailto:satogata@jlab.org"><satogata@jlab.org></a></td>
</tr>
<tr>
<th align="RIGHT" valign="BASELINE" nowrap="nowrap">Organization:
</th>
<td>Jefferson Lab</td>
</tr>
<tr>
<th align="RIGHT" valign="BASELINE" nowrap="nowrap">To: </th>
<td>Hovanes Egiyan <a class="moz-txt-link-rfc2396E" href="mailto:hovanes@jlab.org"><hovanes@jlab.org></a></td>
</tr>
<tr>
<th align="RIGHT" valign="BASELINE" nowrap="nowrap">CC: </th>
<td>Alexandre Deur <a class="moz-txt-link-rfc2396E" href="mailto:deurpam@jlab.org"><deurpam@jlab.org></a></td>
</tr>
</tbody>
</table>
<br>
<br>
<pre>Hi Hovanes,
I have been pondering the "negative curvature" problem in the 5C11/5C11B
and radiator harp scans. I think that the underlying problem is that the
three measurements are quite far away from the expected beam size minimum
(near L=16+75~90m downstream of the 5C11 harp). This means that we are
attempting to fit a parabola with three points that are very far out one
side of the parabola, which is of course outrageously sensitive to relative
errors on the three data points.
I worked through some expected beam behavior and think that this data is
fairly straightforward to reproduce with a few reasonable assumptions:
- We know the incoming beam emittances (which were measured at 5C00)
- The local curvature in the region of measurements is small enough
that the beta function behavior can be approximated as linear rather
than quadratic.
Given these, I have worked through the existing measurements (getting
error bars strictly from statistics) to find the waist positions
(in distance downstream of the 5C11 harp, which should be about 90m
to be centered at the collimator):
L_min(x) = 70+/-8m
L_min(y) = 36+/-8m
sigma_min(x) = 342+/-42 um
sigma_min(y) = 338+/-68 um
So beam is probably a bit big and the focal point is still a bit
upstream of where we would like it. I'll work up some statistics
based on the measured error bars to firm these up, and will write
up a tech note to document this approach. I think this should give
us a much more reasonable handle on the beam convergence at the
radiator, and projected spot sizes on the collimator face.
-Todd
--------------+---------------------------+----------------+------------------
Todd Satogata | CASA Group, Jefferson Lab | (631) 807-0674 | <a class="moz-txt-link-abbreviated" href="mailto:satogata@jlab.org">satogata@jlab.org</a>
--------------+---------------------------+----------------+------------------
</pre>
<br>
</div>
<br>
</body>
</html>